An aluminum electrolytic capacitor is used in various electronic devices. The biggest characteristic of the aluminum electrolytic capacitor is in the capacitance per unit volume larger than that of other capacitors such as a ceramic capacitor. Achieving a large capacitance of the aluminum electrolytic capacitor is largely dependent upon the specific surface area of an aluminum electrode foil. Therefore, in general, an aluminum electrode foil is subjected to an electrochemical or chemical etching process so as to increase an effective specific surface area. Furthermore, in order to increase the surface area expansion rate, which represents an amount of the surface area per unit volume, an etching method has been improved for increasing the density of the number of etching pits and increasing the depth and thickness of the etching pit.
For example, Japanese Patent Unexamined Publication No. S62-62890 discloses an improvement in an etching method. According to the disclosure, etching is carried out after ink including a metal nobler than aluminum, which becomes an etching core, is printed in dots on the surface of an aluminum electrode foil, and thus etching starting points are controlled.
However, in the above-mentioned conventional technology, since aggregation or segregation of the metal nobler than aluminum occurs, it has been difficult to obtain uniformly and finely controlled etching starting points.